1. Field of the Invention
The invention concerns processes for the production of butt joints.
2. Description of the Related Art
A butt joint of this type is known from EP 868 624 B1. In these known butt joints a connecting flange is formed unitarily, as one piece, in the material of the pipe end of each of the respective abutting pipe ends. In comparison to connecting flanges seated separately upon the pipe ends, such a design has great advantages, such as 0-leakage, low flow resistance and low noise generation, as well as improved ability to clean and improved hygiene, as a consequence of their flat internal walls. For these advantages one must however accept the following disadvantages. By the one piece forming on of the connecting flange, the wall thickness and therewith the stability of the connecting flange is necessarily correlated with the wall thickness of the pipe itself. If then higher demands are placed upon the stability of the flange connection, this can not be achieved without increasing the wall thickness of the pipe segment over its entire length, even though this thickening of the pipe itself was not even necessary. In the case of connecting flanges seated upon the pipe end, the wall thickness thereof accordingly also always represents a multiple of the pipe wall thickness.
This increasing of the wall thickness over the entire pipe length doubtless represents a great economical disadvantage, since the material costs represent a large proportion of the cost of manufacture of the pipe. There are also technical disadvantages, since the greater pipe wall thickness represents a greater pipe weight and this weight places greater stresses upon the suspension and the flange connection. The formed-on connecting flanges are often subjected to a strong axial pull-forces. Most often this occurs with vertical running pipelines, however it also occurs in horizontal pipelines as a consequence of the respectively selected separation between two sequential suspensions or free lengths of the pipe. In the case of strong axial pull-forces on a butt joint with connecting flanges formed as one piece on the pipes, it is often the curve apex (area at which the connecting flange and the straight pipe join) which is the weakest point. Upon overloading, there results therewith at this point a conical gap between the contacting connecting flanges. Such a gap destroys any advantage of the formed-on connecting flanges. The pipeline inner surface is no longer continuously flat or flush at this gap location. Fibers and dirt can collect and build up at the gap. Thereby the flow resistance, the noise formation and the ability to clean are made worse. Further, a greater leakage can only be prevented when a seal is applied to the outer flange edge. A pretensioning of the connecting flange by a stronger bending of the ring shaped flange part projecting from the flange beyond 90° brings about only a limited improvement of the flange stability.
This weakness can naturally be improved with the known, relatively new technique of “Tailored Blanks”. When using this technique short pipe pieces of thicker material can be welded to the ends of the pipe sections and the connecting flange can be formed therefrom. This possible embodiment is however completely uneconomical, since it would already be much simpler to weld on an already completely finished bent connecting flange.